Four patients with chronic advanced periodontitis participated in this study. At least one mandibular first molar had to have a hopeless periodontal and prosthetic prognosis. Clinical measurements were made, and the furcation defects were surgically exposed. A notch was placed through the calculus on both the mesial and distal roots. The furcal area was root planed with diamond-tip ultrasonic instruments. The furcations were grafted with a combination of recombinant human platelet-derived growth factor and beta tricalcium phosphate. A collagen barrier for guided tissue regeneration was used on both the facial and lingual surfaces. The flaps were coronally positioned and sutured. All patients were followed at 2-week intervals for 6 months. At 6 months, all teeth demonstrated a reduction in probing depth and a gain in clinical attachment. One tooth demonstrated a Class II furcation involvement, while through-and-through furcation involvement was still evident on the other three experimental teeth. The teeth were removed en bloc and processed for histologic evaluation. Three root surfaces demonstrated periodontal regeneration, an additional three showed new attachment, and one surface revealed junctional epithelium as measured from the base of the calculus notch. The notch area could not be identified on one surface of one specimen.